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Abstract:

A Bandwidth Manager, BM, entity connectable to a Bandwidth Manager system
(300) adapted to serve clients having knowledge about performed resource
reservations and including a plurality of Bandwidth Manager, BM, entities
hierarchically connected in multiple levels, wherein one or more BMs
is/are located at each level. The BM entity includes elements for
synchronizing states of BM entities located at a level higher than the
level of the BM entity, wherein at least two BM entities at the higher
level are workers.

Claims:

1. A Bandwidth Manager, BM, entity connectable to a Bandwidth Manager
system (300) adapted to serve clients having knowledge about performed
resource reservations and comprising a plurality of Bandwidth Manager,
BM, entities hierarchically connected in multiple levels, wherein one or
more BMs is/are located at each level, characterised in that the BM
entity comprises means for synchronising states of BM entities located at
a level higher than the level of said BM entity, wherein at least two BM
entities at the higher level are workers.

2. The Bandwidth Manager BM entity according to claim 1, characterised in
that the BM entity is arranged to handle negative reservation offsets
indicative of expired resource reservations in a BM entities wherein the
reservation may be booked in another BM entity.

3. The Bandwidth Manager BM entity according to claim 1, characterised in
that the BM entity is arranged to handle positive reservation offsets
indicative of the amount of resources that is returned to or updated in a
worker BM but that is previously booked in another worker BM at the same
level.

4. The Bandwidth Manager BM entity according to claim 3, characterised in
that the BM entity is arranged to handle a remove message terminating a
reservation before it is automatically aborted as its life times out to
create the positive reservation offset.

5. The Bandwidth Manager BM entity according to claim 3, characterised in
that the BM entity is arranged to handle an update message extending the
lifetime of an existing reservation by creating a positive reservation
offset and establish a new reservation state.

6. The Bandwidth Manager BM entity according to claim 2, characterised in
that the BM entity is arranged to report the reservation offsets
downwards stepwise in the hierarchy of BMs.

7. The Bandwidth Manager BM entity according to claim 6, characterised in
that the BM entity is arranged to issue the report immediately as the
event causing the reservation offset to be created occurs, issue the
report after a period allowing multiple offsets to be aggregated into
single reports, or issue the report periodically.

8. The Bandwidth Manager BM entity according to claim 7, characterised in
that the BM entity is arranged to send the report within the refresh
interval of the reservations made with the next lower BM entity.

9. The Bandwidth Manager BM entity according to claim 7, characterised in
that the BM entity is arranged to receive reservation offset reports, to
acknowledge them upwards and to create their own reservation offsets.

10. The Bandwidth manager, BM, according to claim 1, characterised in that
the BM entity is implemented by computer program product.

11. A method in a Bandwidth manager, BM, entity connectable to a Bandwidth
Manager, BM, System (300) adapted to serve clients having knowledge about
performed resource reservations and comprising a plurality of Bandwidth
Manager, BM, entities hierarchically connected in multiple levels,
wherein one or more BMs is/are located at each level, characterised in
that the method comprises the step of:synchronising states of BM entities
located at a level higher than the level of said BM entity, wherein at
least two BM entities at the higher level are workers.

12. The method according to claim 11, characterised in that the method
comprises the further step of:creating negative reservation offsets
indicative of expired resource reservations in a BM entities wherein the
reservation may be booked in another BM entity.

13. The method according to claim 11, characterised in that the method
comprises the further step of:creating positive reservation offsets
indicative of the amount of resources that is returned to or updated in a
worker BM but that is previously booked in another worker BM at the same
level.

14. The method according to claim 13, characterised in that the method
comprises the further step of:handling a remove message terminating a
reservation before it is automatically aborted as its life times out to
create the positive reservation offset.

15. The method according to claim 13, characterised in that the method
comprises the further step of:handling an update message extending the
lifetime of an existing reservation by creating a positive reservation
offset and establish a new reservation state.

16. The method according to claim 12, characterised in that the method
further comprises the step of:reporting the reservation offsets downwards
stepwise in the hierarchy of BMs.

17. The method according to claim 16, characterised in that the method
comprises the further step of:issuing the report immediately as the event
causing the reservation offset to be created occurs, orissuing the report
after a period allowing multiple offsets to be aggregated into single
reports, orissuing the report periodically.

18. The method according to claim 17, characterised in that it comprises
the further step of:sending the report within the refresh interval of the
reservations made with the next lower BM entity.

19. The method according to claim 17, characterised in that it comprises
the further step of:receiving reservation offset reports, to acknowledge
them upwards and to create their own reservation offsets.

20. A computer program product directly loadable into the internal memory
of a computer within a router or server in a data network, comprising the
software code portions for performing the steps of claim 11.

21. A computer program product stored on a computer usable medium,
comprising readable program for causing a computer, within a router or
server in a data network, to control an execution of the steps of claim
11.

22. A Bandwidth Manager system (300) adapted to serve clients having
knowledge about performed resource reservations and comprising a
plurality of Bandwidth Manager, BM, entities hierarchically connected in
multiple levels, wherein one or more BMs is/are located at each level,
characterised in that the BM system comprises means for synchronising on
behalf of upper BMs located on a higher lever, wherein at least two BM
entities at the higher level are workers.

23. The Bandwidth Manager system according to claim 22, characterised in
that the BM system is arranged to handle negative reservation offsets
indicative of expired resource reservations in a BM entities wherein the
reservation may be booked in another BM entity.

24. The Bandwidth Manager system according to claim 22, characterised in
that the BM system is arranged to handle positive reservation offsets
indicative of the amount of resources that is returned to or updated in a
worker BM but that is previously booked in another worker BM at the same
level.

25. The Bandwidth Manager system according to claim 24, characterised in
that the BM system is arranged to handle a remove message terminating a
reservation before it is automatically aborted as its life times out to
create the positive reservation offset.

26. The Bandwidth Manager system according to claim 24, characterised in
that the BM system is arranged to handle an update message extending the
lifetime of an existing reservation by creating a positive reservation
offset and establish a new reservation state.

27. The Bandwidth Manager system according to claim 23, characterised in
that the BM system is arranged to report the reservation offsets
downwards stepwise in the hierarchy of BMs.

28. The Bandwidth Manager system according to claim 27, characterised in
that the BM system is arranged to issue the report immediately as the
event causing the reservation offset to be created occurs, issue the
report after a period allowing multiple offsets to be aggregated into
single reports, or issue the report periodically.

29. The Bandwidth Manager BM system according to claim 28, characterised
in that the BM system is arranged to send the report within the refresh
interval of the reservations made with the next lower BM entity.

30. The Bandwidth Manager system according to claim 28, characterised in
that the BM system is arranged to receive reservation offset reports, to
acknowledge them upwards and to create their own reservation offsets.

Description:

FIELD OF THE INVENTION

[0001]The present invention relates to a method and arrangements in a data
network. In particular, the present invention relates to a Bandwidth
Manager (BM) system, a BM and a method that prevent overbooking of
network resources in the data network.

BACKGROUND

[0002]A current networking trend is to provide "Internet Protocol (IP) all
the way" to wired and wireless units in an IP based data network.
Objectives include simplifying the infrastructure, supporting a wide
range of applications, and meeting diverse user demands on the
communication service. Satisfying these objectives requires scalable and
reliable solutions are needed providing service differentiation and
dynamic bandwidth management within IP networks.

[0003]IP was from the beginning designed to be a general communication
solution. IP technology is now recognised to be cheap and appropriate for
supporting both traditional data applications and delay-sensitive
real-time data applications. To provide expected service for real-time
applications, logically (and physically) separate IP networks are used.

[0004]Each IP network serves only a subset of sensitive applications (e.g.
IP telephony) with quite predictable bandwidth requirements. By limiting
the range of applications, the total bandwidth demand can be predicted.
This allows for the network to be dimensioned using the same traffic
models as are used for vertically optimised networks. The benefit of
cheap IP equipment is obtained without requiring support for dynamic
service provisioning in the IP technology.

[0005]Network operators now aim at cutting the overhead cost of
maintaining several parallel networks. One current trend is to simplify
the infrastructure by running all kinds of applications, with various
network service demands, in the same logical IP network (i.e. next
generation multi-service networks). This means that the application
heterogeneity in IP networks is increasing.

[0006]In the research and standardisation bodies the development of QoS
support has progressed from providing signalled solutions for the
Internet (somewhat resembling the solutions used in vertical networks) to
now recognising that more stateless solutions are favourable.

[0007]The scalability problems of solutions using per-flow QoS management
in routers have resulted in the differentiated services architecture
defined by the IETF. The objective with this architecture is to provide
scalable QoS support without requiring per-flow state in routers. The
basic idea is that IP packet headers include a small label (known as the
DiffServ field) that identifies the treatment (per-hop behaviour) that
packets should be given by the routers. Consequently, core routers are
configured with a few forwarding classes and the labels are used to map
packets into these classes. The architecture relies on packet markers and
policing functions at the boundaries of the network to ensure that the
intended services are provided.

[0008]One advantage of differentiated services is that the model preserves
the favourable properties that made the Internet successful; it supports
scalable and stateless forwarding over interconnected physical networks
of various kinds. The standard model is, however, limited to
differentiated forwarding in routers and therefore the challenge lies in
providing predictable services to end users.

[0009]Qualitative services (relatively better than best-effort services,
but depending on where the traffic is sent and on the load incurred by
others at the time) can be provided by relying only on DiffServ support
in routers and bandwidth management mechanisms for semi-static admission
control and service provisioning.

[0010]To provide quantitative (minimum expectation) service, resources
must be dynamically administrated by bandwidth management mechanisms and
involve dynamic admission control to make sure that there are sufficient
resources in the network to provide the services committed.

[0011]The entity performing dynamic admission control is in this
specification called a bandwidth manager (BM). The BM is adapted to keep
track of the available network resources and performs admission control
on incoming resource reservation requests from clients. Clients to a
bandwidth manager are typically call servers emulating the traditional
telephony service and various broadband application frameworks providing
services such as video on demand, video telephony, and gaming. These
clients are commonly referred to as application frameworks (AFs) and the
term AF is also used in this specification to denote the clients to the
BM.

[0012]A reservation request from an application framework to a BM
typically include the amount of bandwidth needed, a description of the
forwarding quality expected, and endpoint identifiers for the target data
stream in the form of IP addresses. Such request may also include
additional arguments such as start and stop times for the reservation.

[0013]To perform admission control the BM stores a history of previously
admitted resource reservations. The BM takes decisions to admit new
resource requests based on the total amount of available resources, the
amount currently reserved by previously reservations and the amount of
resources requested in the new resource request.

[0014]The BM should provide accurate resource control both in access
domains and in core domains. Accurate resource control requires the BM to
control resources at individual contention points in the network.
Contention points in a network are those points at which multiple data
streams share forwarding capacity. Examples include outgoing network
interfaces, tunnel heads in MPLS networks, and VC/CP entrances in ATM
networks.

[0015]When deployed in large data networks that may include multiple
network domains the BM system needs to be distributed for performance,
scalability and reliability reasons. This means that BM instances may be
distributed on a set of hardware platforms. These instances must
communicate to serve AFs with resource reservation services in the
different network domains covered by the BM system. Examples are
described on how a set of BM instances can be arranged in distributed BM
systems. FIG. 1 shows a BM deployment comprising a plurality of AFs
100a-f. The AF 100 a,b are connected to the top level BM 102 a, the AFs
100 c,d are connected to the top level 102b and the AFs 100 e,f are
connected to the top level 102c. The top-level BMs are further connected
to the sub-network BMs 104a-c. The example shown in FIG. 1 cover
bandwidth management in access 106,108,110, backhaul 112, core 116 and
interconnect 120 domains. The access network comprises a Customer
Premises Equipment (CPE) 108 and an end-terminal 106. The backhaul
network 112 and the core network 116 are connected via an IP edge 114 in
the same way as the core network 116 and the interconnect network 120
that are connected via the IP edge denoted 118.

[0016]BMs (instances) can be scaled in a hierarchical manner as shown in
FIG. 1, whereby BMs at each level in the hierarchy reserve resources from
lower level BMs. Lower level BMs are responsible for different
sub-domains of the network. Such BMs are referred to as sub-network BMs
denoted S-BMs. Top-level BMs are responsible for identifying the
sub-network that the session crosses and hence the sub-network BMs that
must be queried for resources. FIG. 2 illustrates a BM deployment as in
FIG. 1 with the difference that the sub network BMs may request resources
from another BM in an adjacent peer domain as indicated by the arrows 202
and 204.

[0017]In a distributed BM system mechanisms are provided for automatically
finding the right BMs across the layers in the hierarchy and between
peers. Thereby an AF does not need to understand the underlying network
topology. Finding the appropriate BM is achieved by using "source
seeking" BMs. Such BMs take requests from initiating BMs and forward them
to the BM being responsible for performing the reservation.

[0018]For the hierarchical model multiple top-level BMs interact with AFs.
Each AF may have a designated top-level BM which provides a high level
routing and distribution function, identifying the sub-network hops that
the data stream must traverse. Top-level BMs then pass requests to
sub-network BMs which are responsible for reserving resources in
individual networks.

[0019]Because of the topology model and the routing function of the
top-level BM, all hops of the reservation, originating access, core,
terminating access can be derived from the top-level BM. In any
architecture there can be multiple top-level BMs since no single
top-level BM needs to understand the state of the reservations of the
others.

[0020]Below the top-level BM multiple sub-network bandwidth managers are
provided which map the reservation requests to the underlying network
resources. These BMs take reservation requests from multiple top-level
BMs and perform Call Admission Control (CAC) based on the occupancy of
the network resources.

[0022]Scaling of reservation request load is obtained by deploying
multiple top-level BMs. Bandwidth for individual sessions/calls are
requested from the top-level BMs, which share aggregate resources in
their domain by interacting with lower level BMs for requesting
(pre-allocating) bandwidth aggregates.

[0023]Scaling to arbitrary large topologies is obtained by deploying
several BMs at the bottom layer responsible for different topological
sub-domains inside the domain. BMs may be configured to allocate
(aggregate) resources with BMs in adjacent (peering) sub-domains an
additional dimension of scale is achieved. By combining the hierarchical
model with peering as shown in FIG. 2, each top-level BM does not have to
interact with each BM of the sub-domains. This effectively results in
adding more levels to the hierarchy.

[0024]In the peering model the correct "source" BM for a session must be
identified as it is responsible for initiating any requests to peer BMs.
In order to hide the network topology of the bandwidth management layer
to the AF layer, the AF does not need to know where the source BM for
each reservation is specifically located. The AF only needs to initiate a
request to any BM and the request will be transferred to the source BM
via a source seeking BM process, so that a normal process of the request
for resources can be started.

[0025]In the example system architectures described in the previous
section, top-level BMs need to communicate directly or indirectly with
other BMs to allocate aggregate bulk resources that can be offered to
AFs. Bulk resources may also need to be allocated between the BMs
arranged in a hierarchy as shown in FIG. 1 or between peering BMs as
shown in FIG. 2. Naturally, the BMs need also to return bulk resources
that are not needed in the near future. Note that the chain of BMs
involved in allocating bulk resources can include two or more BMs
arranged in hierarchy or as peers. A reservation for bulk resources made
by a given BM is an amount of resource allocated for an aggregate of
reservations maintained by the BM. Such a bulk reservation can be made by
a BM in advance to prepare for future reservation request arriving, or
immediately as reservations are requested in the BM.

[0026]By allocating resources in bulk for aggregates of reservations,
top-level BMs can immediately grant reservation requests made by
application frameworks. This is attractive since it allows the system to
offer short response times for such requests.

[0027]Bulk resources can be allocated between BMs for individual
contention points, for individual paths through a network domain, or for
network domains. Contentions points, paths, and networks can all be
represented as objects for which resources can be allocated. Such objects
are referred to as resource objects in this specification.

[0028]A distributed BM system can implement different resilience
strategies. Resilience means protection against failure, the ability to
recover from different failure situations.

[0029]Standby BM instances may keep up-to-date information on network
resources represented as resource objects (hot standbys), or may need to
acquire such information when activated (warm standbys). Standby nodes
not having BM instances up running are commonly referred to as cold
standbys.

[0030]Hot standby BMs may maintain reservation states for a backed up
worker in addition to the information on network resources being kept
hot, or rely on that such information is loaded into the standby at
failover. Information on reservation states can be loaded through
auditing. E.g. in a hierarchical BM system such as those shown in FIG. 2
and FIG. 1, a hot S-BM standby being activated may audit the top-level
BMs to re-establish the reservation states of the S-BM it was backing up.
Real time synchronisation is required for hot standbys in order to
achieve seamless failover from an active node to a standby node. A worker
is an instance that is currently active in serving its clients.

[0031]BMs at the same level in a hierarchical BM system can be arranged
such that all, or a plurality of BMs are workers. It is advantageous to
have a plurality of workers at the same level, since clients may contact
any BM of the worker BMs. It is then possible to share the load between
the worker BMs and the client may change BMs seamlessly, also for active
sessions. All BMs in a set of workers should at any time be capable of
serving any other BM at the level above or, when the set of BMs
constitutes the top-level, any AF requesting resources. This requires
that resource bookings made in these BMs are synchronized in real time to
ensure that resources are not overbooked. Overbooking implies that
resources related to one request are reserved more than once. A
disadvantage is that the real time synchronisation requires continuous
connectivity and such a system will therefore fail during connectivity
failure.

[0032]Therefore, it would be desirable to be able to prevent overbooking
in a BM system having at least two BMs at one or more levels arranged as
workers without relying on real time synchronisation. If real time
synchronisation is avoided the BM system is able to protect against
overbooking in failure scenarios including connectivity failure between
BMs.

SUMMARY OF THE PRESENT INVENTION

[0033]Thus, the object of the present invention is to provide means that
is able to prevent overbooking even during connectivity failure between
BMs.

[0034]The objective of the present invention is achieved by the system of
claim 1, by the method of claim 11, by the computer program product of
claims 20 and 21 and by the system of claim 22.

[0035]Preferred embodiments are defined by the dependent claims.

[0036]According to a first aspect, the present invention relates to a
Bandwidth Manager, BM, entity connectable to a Bandwidth Manager system
adapted to serve clients having knowledge about performed resource
reservations and comprising a plurality of Bandwidth Manager entities
hierarchically connected in multiple levels, wherein one or more BMs
is/are located at each level. The BM entity comprising means for
synchronising states of BM entities located at a level higher than the
level of said BM entity, wherein at least two BM entities at the higher
level are workers makes it possible to prevent overbooking even during
connectivity failure between BMs.

[0037]According to a second aspect, the present invention relates to a
method in a Bandwidth manager, BM, entity connectable to a Bandwidth
Manager, BM, System (300) adapted to serve clients having knowledge about
performed resource reservations and comprising a plurality of Bandwidth
Manager, BM, entities hierarchically connected in multiple levels,
wherein one or more BMs is/are located at each level. The method
comprising the step of synchronising states of BM entities located at a
level higher than the level of said BM entity, wherein at least two BM
entities at the higher level are workers, makes it possible to prevent
overbooking even during connectivity failure between BMs.

[0038]According to a third aspect, the present invention relates to a
Bandwidth Manager system (300) adapted to serve clients having knowledge
about performed resource reservations and comprising a plurality of
Bandwidth Manager, BM, entities hierarchically connected in multiple
levels, wherein one or more BMs is/are located at each level. The BM
system comprising means for synchronising on behalf of upper BMs located
on a higher lever, wherein at least two BM entities at the higher level
are workers, makes it possible to prevent overbooking even during
connectivity failure between BMs.

[0039]According to fourth aspect, the present invention relates to a
computer program product directly loadable into the internal memory of a
computer within a router or server in a data network, comprising the
software code portions for performing the steps of the method.

[0040]According to fifth aspect, the present invention relates to a
computer program product stored on a computer usable medium, comprising
readable program for causing a computer, within a router or server in a
data network, to control an execution of the steps of the method.

[0041]Synchronising states transferred in real time between BMs consumes
forwarding resources, processing capacity and memory in BM nodes. Hence,
an advantage of the present invention is that the present invention
enables a stronger solution for resilience at lower cost compared to one
that requires state synchronisation in real time between BMs at the same
level.

[0042]A further advantage of the present invention is that the problem of
recovering bandwidth after failure is solved by the introduction of
reservation offsets, which allows most bandwidth for which reservation
states are lost to be immediately reused without risking bandwidth
overbooking. Avoiding bandwidth overbooking is essential since guarantees
or assurances on forwarding quality otherwise will be violated.

[0045]FIG. 3 discloses synchronisation points for all BM worker resilience
according to the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0046]The present invention will now be described more fully hereinafter
with reference to the accompanying drawings, in which preferred
embodiments of the invention are shown. This invention may, however, be
embodied in many different forms and should not be construed as limited
to the embodiments set forth herein; rather these embodiments are
provided so that this disclosure will be thorough and complete, and will
fully convey the scope of the invention to those skilled in the art. In
the drawings, like numbers refer to like elements.

[0047]The present invention according to the first aspect relates to a
Bandwidth manager (BM) entity adapted to be a part of a BM system
comprising a plurality of BMs hierarchically connected in multiple
levels, wherein one or more BMs is/are located at each level. A BM is
typically realised by software means and may be implemented in
conventional routers and servers in a conventional data network 100
comprising interconnected routers 110 and servers.

[0048]An example of such a conventional network is a multi-technology
network where an operator provides an IP/MPLS backbone and several access
networks based on various switched link layer technologies e.g.,
including an access network based on ATM switching, another access
network based on Ethernet switching and a third based on WLAN
technologies. Moreover, the network may comprise interconnectable
routers, servers and other network elements known by a man skilled in the
art.

[0049]In this application, a data network is defined as a switched network
forwarding data units between network interfaces of network nodes using
identifiers associated with the target circuit being setup through the
network e.g., as in Asynchronous Transfer Mode (ATM networks and in
Multiprotocol Label Switching (MPLS) networks, or a datagram network
forwarding data units between network interfaces of network nodes using
global addresses enabling local next-hop decisions made by each node
e.g., as in Internet Protocol (IP) networks. The data units may be of
fixed size e.g., ATM cells or of variable size e.g., IP packets using
their destination addresses for datagram forwarding or using MPLS tags
for switching.

[0050]The invention according to the present invention provides means for
preventing overbooking wherein the synchronisation between BMs needed for
resilience at levels where several BMs are workers is not required to be
performed in real time.

[0051]Real time synchronisation is not necessary since the present
invention utilizes that the clients have knowledge about resource
reservations previously performed. Based on that knowledge, the clients
are able to send messages associated with previous performed
reservations. The messages create offsets that are used for managing a
synchronisation procedure according to embodiments of the present
invention, which is further described below. This synchronisation
procedure is not required to be performed in real time.

[0052]The synchronisation procedure is performed by BMs at a level
directly below the BM worker level, or several levels below such worker
level. FIG. 3 illustrates a BM system 300 comprising BMs managing
resources for AFs 302a-e. The AFs are connected to top-level BMs a-c that
are further connected to intermediate-level BMs d-e. The
intermediate-level BMs d-e are further connected to a sub-network BM f.
As illustrated, in FIG. 3, the intermediate-level BM "d" can synchronise
states for top-level BMs "a", "b" and "c" given that all of the
intermediate-level BMs "d" and "e" are not workers. Sub-network BM "f"
can synchronise states for all other BMs. A BM capable of synchronising
on behalf of upper BMs is referred to as a state synchronisation BM
(SS-BM). SS-BMs cannot be WR-BMs and are thus instead typically backed up
by a standby BM.

[0053]The present invention is based on that (1) all reservations have a
limited lifetime. The life time of a reservation is referred to as the
refresh interval. Also, the invention presumes that (2) AFs and BMs (i.e.
top-level and intermediate level BMs) provide complete reservation
information in insert and update messages. The first message issued when
requesting a reservation is referred to as an insert, while messages
extending the lifetime of an existing reservation are referred to as
updates. According to an embodiment of the present invention, a remove
message is introduced. The remove message makes it possible to
effectively terminate reservations before they are automatically aborted
as their life times out. The remove and update messages create the above
mentioned offsets.

[0054]The essential parts of the complete reservation information are
typically the amount of requested resources, the endpoints of the
reservation, and for updates and removes, a reservation ID possibly
accompanied with an authentication token. An authentication token is a
type of code used to guarantee that a message is sent from an entitled
unit. The code may be connected to a part of the message. The
authentication token may be needed when AFs or upper level BMs cannot be
trusted. Additional information may also be included. In general, the
concept requires that the same information given in inserts that creates
any form of state in the BM system must be provided also in updates and
removes.

[0055]The reservation ID is typically created by a BM receiving an insert
message. The ID is then sent back to the entity issuing the insert as
part of an acknowledgement granting the reservation request. Replies to
rejected reservation requests do not need to include a reservation ID.

[0056]As mentioned above, AFs, top-level BMs and intermediate level BMs
may request resources from a level at which a plurality of BMs are
workers. In this specification it is hereafter referred to such
requesters as requesting entities (REs) and BMs at a level where several
BMs are workers as worker resilient BMs (WR-BMs).

[0057]Based on (1) and (2), enough state synchronisation to prevent
overbooking of resources can be obtained through what is herein referred
to as reservation offsets, as mentioned above. A reservation offset is
directly associated with a resource object. The BM according to
embodiments of the present invention is adapted to manage such
reservation offsets.

[0058]A negative reservation offset keeps track of resource reservations
that have expired in a BM for the RE that established the reservation but
may be booked in another BM (i.e. the other BM may have taken over the
reservation). A positive reservation offset is the amount of resources
that is returned to or updated in a WR-BM but that is previously booked
in another WR-BM at the same level, i.e. the WR-BM getting the resource
reservations removed or updated has no reservation state associated with
them, since the insert messages that created the reservations was sent to
another WR-BM.

[0059]When one or more WR-BMs fail or when a RE change the WR-BM to
interact with, REs may send updates and removes to another WR-BM but the
one at which their current reservations are inserted, i.e. the failed
WR-BM. Unknown updates and removes are identified by that the reservation
ID of these messages are unknown by the WR-BM receiving them.

[0060]The reservation offsets is according to embodiments of the present
invention created by using the messages remove and update. A remove gives
a positive offset that may be used for a new reservation and an update
gives a positive offset plus a new reservation. That implies that an
update is interpreted as a remove plus an insert. Hence, a WR-BM
receiving unknown updates or removes accepts them and creates positive
reservation offsets for the involved resource objects. Update messages
for reservations not previously inserted in the WR-BM receiving those
results further in that bandwidth is allocated for the involved resource
objects. Allocating this bandwidth is always possible since positive
offsets effectively increase the amount of resources available for
booking. This means that resources returned through removes immediately
becomes available for new reservations requested using insert messages.

[0061]As indicated above, negative reservation offsets are created when
reservations have expired in a BM for the RE that established the
reservation but may be booked in another BM. Negative offsets hence keep
track of resources retained through timer expiration, while positive
offsets keep track of resources returned through updates or removes. Note
that expired bandwidth in a BM is no longer available. Hence, even if a
BM for which a booking expires in a lower-level BM remains operational,
the expired bandwidth cannot be used.

[0062]Reservations offsets, both positive and negative, are reported
downwards stepwise in the BM hierarchy i.e. level by level until they
reach the SS-BM responsible of synchronizing states for the WR-BMs that
reserve the resources of the resource object for which the offset is
maintained. Such reports may be issued immediately as the event causing
the reservation offset to be created occurs, after a period allowing
multiple offsets to be aggregated into single reports, or periodically to
allow for both aggregation and controlled signalling rates between BM
levels. In all cases reports need to be sent within the refresh interval
of the reservations made with the next lower BM.

[0063]Before being reported downwards in the BM hierarchy, negative and
positive reservation offsets may even out each other completely or
partly. E.g., considering the structure of BMs shown in FIG. 3, say that
a top-level WR-BM sends a remove message to an intermediate-level WR-BM.
This intermediate-level WR-BM then creates a positive offset for a
resource object. However, before this WR-BM reports the positive offset
downwards to the sub-network SS-BM another reservation with the same
resource object expires and a negative reservation offset is created. If
these offsets are equal in size they will even each other out. Otherwise
only the difference between them will be kept by the intermediate WR-BM
as a negative or positive reservation offset, which eventually may be
reported downwards to the SS-BM.

[0064]Each BM receiving reservation offset reports acknowledges them
upwards and creates their own reservation offsets. When the reservation
offsets are reported all the way down to an SS-BM they only exist in this
SS-BM. Note that intermediate BMs between the up most WR-BM level and the
SS-BM may or may not themselves be WR-BMs.

[0065]In SS-BMs reservation offsets must be kept until all active
reservations made by the REs are guaranteed to have expired, been
updated, or removed. This means that reservation offsets in SS-BMs must
have refresh intervals (lifetimes) long enough to provide this guarantee.
The value of a refresh interval for reservation offsets in an SS-BM
depends on all the refresh intervals of reservations made by AFs and all
BMs above the SS-BM in the hierarchy.

[0066]Maintaining negative and positive reservations offsets allows the BM
system to use some of the resources allocated by failed or abandoned
WR-BMs that otherwise would have been locked by such WR-BMs. I.e.
returned resources may be used immediately by new reservations and
resources having updated reservations do not have to reserve new
resources but may automatically use the already reserved resources. Since
the WR-BM may pre-allocate resources the complete amount of resources
allocated by such WR-BMs may however not be available until reservation
offsets times out in SS-BMs. This means that all negative offsets cannot
be used by positive offsets when a WR-BM has pre-allocated resources.
Remaining negative reservation offsets becomes available only after such
offset has expired. I.e., positive and negative offsets are reported to a
SS-BM and a WR-BM may reserve more resources compared to the reserved
resources of its clients, which implies that the negative and the
positive offsets are not equal. In this case, the remaining offsets are
negative corresponding to the resources reserved by the WR-BM in excess
to the resources reserved by the clients. Thus, these resources become
available first when the remaining negative offset has expired. Note that
only negative offsets may remain upon expiration. Positive offsets will
then always have been cancelled by equally sized or larger negative
offsets. Upon expiration in an SS-BM, negative offsets appear as
resources, e.g. bandwidth, returned to the SS-BM.

[0067]In the drawings and specification, there have been disclosed typical
preferred embodiments of the invention and, although specific terms are
employed, they are used in a generic and descriptive sense only and not
for purposes of limitation, the scope of the invention being set forth in
the following claims.